Seat back



FIG. 1 is a perspective view of a seat back in accordance with our design with a chair which forms the environment of the seat back and forms no part of the claimed design, the chair or portions thereof being shown in broken lines for illustrative purposes only.

FIG. 2 is an enlarged front elevational view thereof;

FIG. 3 is an enlarged rear view thereof;

FIG. 4 is an enlarged right-side elevational view thereof, with the left-side elevational view being a mirror image thereof;

FIG. 5 is an enlarged top plan view thereof; and,

FIG. 6 is an enlarged bottom view thereof. 

The ornamental design for a seat back, as shown and described. 